Field
Embodiments of the present invention relate to a seismic isolation apparatus and a seismic isolation method.
Description of the Related Art
Seismic isolation devices have been introduced as earthquake countermeasures for structures, such as buildings, machines and equipment. The seismic isolation apparatus is generally composed of a soft member such as a laminated rubber, and an attenuation member such as an oil damper to prevent earthquake acceleration from being transmitted to a structure. The general seismic isolation apparatus composed of the soft member and the attenuation member is not always effective against a large long-period displacement response even if the general seismic isolation apparatus is effective against a short-period displacement response. The general seismic isolation apparatus has difficulty of designing seismic isolation for the large long-period displacement response.
That is, if a large long-period earthquake vibration beyond expectations is received, there is a possibility that a structure provided with a seismic isolation apparatus may break its member such as the laminated rubber due to exceeding a design allowable value.
Each of FIGS. 13 to 16 is a sectional view of a seismic isolation apparatus in accordance with examples of conventional seismic isolation apparatus.
For example, as illustrated in FIGS. 13 and 14, in order to cope with breakage in an elastic body 100 such as a laminated rubber, between a structure 101 and a foundation 102, there is an example (which will be referred to as “first example”) of the seismic isolation apparatus that includes a bed slide 103 fixed to the elastic body 100 and the structure 101, an upper support body 104 that is brought into contact with the bed slide 103 if there is large displacement, a lower support body 106 composed of layer composition such as a rubber plate that elastically supports the upper support body 104, and the like, and in which characteristics of the elastic body 100 that is squeezed in a direction perpendicular to its lamination plane allows the structure 101 to land on the seismic isolation apparatus by using elastic and cushioning action between the upper support body 104 and the lower support body 106 before the elastic body 100 is broken to reduce impact force caused by dropping of the structure 101.
Further, as illustrated in FIG. 15, between the structure 101 and the foundation 102, there is an example (which will be referred to as “second example”) of the seismic isolation apparatus that includes an upper sliding member 104 and a lower sliding member 106, provided with sliding faces so as to surround a periphery of a laminated rubber 100, and in which if the laminated rubber 100 is broken, the upper sliding member 104 and the lower sliding member 106 are brought into contact with each other to slide as well as support self-weight of the structure 101.
Furthermore, as illustrated in FIG. 16, in order to prevent the laminated rubber 100 provided between the structure 101 and the foundation 102 from breaking, there is an example (which will be referred to as “third example”) of the seismic isolation apparatus that has a structure in which if an attachment face of the laminated rubber 100 receives a predetermined load, the laminated rubber 100 slides with respect to the foundation 102.
In the first example, since the lower support body 106 is composed of a rubber plate, and the like, energy generated by dropping of the structure 101 is converted into energy of elastic deformation, and then the energy, as it is, returns to the structure 101 as vibration energy. As a result, in the structure 101, there is a case where the energy generated by the dropping is not absorbed and consumed to cause vertical impulsive vibration. Further, if a number of elastic bodies 100 arranged are unevenly broken to cause a slight inclination to occur in the structure 101, there may be a case where dropping in accordance with an inclination angle is occurred, thereby causing impact force to be hardly absorbed.
The conventional method allowing the laminated rubber 100 to slide is not always effective against three-dimensional displacement in vertical and side-to-side directions even if the conventional method allowing the laminated rubber 100 to slide is effective against displacement in a side-to-side direction. As a result, it may be impossible to absorb impact force generated by the structure 101.
Further, the conventional method which is applied to the first to third examples has a possibility that the structure 101 may violently collide with the upper support body and the upper sliding member 104, the lower support body and the lower sliding member 106, or the like, to cause the members 104 and 106, and the structure 101, to be broken depending on vertical behavior of the structure 101 when the laminated rubber 100 is broken.